Chill injury at alternating temperatures in Orchesella cincta (Collembola : Entomobryidae) and Pyrrhocoris apterus (Heteroptera : Pyrrhocoridae)

Survival and Lt(50) after exposures at constant low temperature were compar ed to the values obtained at alternating temperatures in two active (summer acclimated) temperate terrestrial arthropods. The experimental regimes use d interruptions - daily transfers from the lower temperature to various hig her temperatures for two hours or to one high temperature for Various durat ions. In both species the alternating conditions improved survival, implyin g reparation of the chill injury. In the collembolan Orchesella cincta, the re was a maximum Lt(50) when the higher exposure temperature was equal to t he temperature of rearing (19 degrees C). In the bug Pyrrhocoris apterus, L t(50) increased strongly with increasing higher temperature from 0 to 15 de grees C, and was subsequently constant over the entire physiological range suitable for development (to 35 degrees C). Exposure at 0 degrees C was har mful if continuously applied, but survival increased, relative to a constan t exposure at -5 degrees C, if the temperature alternated between -5 and 0 degrees C.